This invention relates to the recovery of fuel from oil shale. It has particular application to the processing of oil shale mined in Eastern United States; i.e., states like Kentucky and others predominately east of the Mississippi River. It is emphasized that, while this invention is uniquely applicable to Eastern shale, it is not intended that this invention should be in any way restricted to practice only with Eastern shale. To the extent that the teachings presented here are applicable to oil shales from other areas or of other types than those from Eastern United States, such application is within the scope of this invention.
The prior art teaching deals predominantly with oil shale derived from Western United States. Burton U.S. Pat. No. 4,148,710 typifies this prior art teaching. Burton combines pyrolysis and combustion to derive fuel from the shale. The raw shale is pyrolyzed in a fluidized bed by heat derived from gases resulting from the combustion or oxidation of the residual carbon from the spent shale. This spent shale is also maintained in a fluidized bed during combustion.
The following Table I presents an analysis of oil shale from Sunbury, Kentucky:
TABLE I ______________________________________ Sunbury Shale Analysis Westinghouse Electric Corporation* IGT** IMMR*** ______________________________________ Total Carbon, wt. % 17.89 .+-. 0.84 14.71 13.63 Hydrogen 2.08 .+-. 0.05 1.74 1.83 Nitrogen 0.63 .+-. 0.01 0.56 0.61 Sulfur 2.48 .+-. 0.19 3.25 3.16 Oxygen (by difference) 2.07 .+-. 1.12 2.66 Ash 74.85 .+-. 0.29 77.05 100.00 100.00 H/C Atomic Ratio 1.40 .+-. 0.06 1.41 1.61 ______________________________________ *Average of six analyses **Institute of Gas Technology ***Institute of Mining & Mineral Research
The divergence in carbon content between the Westinghouse analysis and the IGT and IMMR analyses could to a large extent result from differences in the material analyzed.
The carbon content in the above table, which is between 13.63% and 18.73% according to Table I, is the total content of carbon in the shale. The total carbonaceous material is called the kerogen. The kerogen includes the oil and vaporous hydrocarbon products and the residual carbon in the shale. The total content of carbon in Western U.S. shale is about the same. The difference between Eastern and Western shale resides in the relative proportions of oil-shale organic carbon recovered as liquid and gaseous fuels. While in Western shales pyrolysis recovers 70-90% of the kerogen as liquid and/or gaseous fuels leaving 30-10% behind as residual carbon, in Eastern shales pyrolysis recovers 30-60% of the kerogen as liquid and gaseous fuels leaving 60-40% as residual carbon. Pyrolysis and combustion for Eastern shales results in a low yield of fuels and either an excess of heat from combustion or a loss of residual carbon in the spent shale. The following Table II shows how the components of the kerogen are distributed in the products of a pyrolysis of Eastern shale:
TABLE II ______________________________________ Sunbury Oil Shale Processing Results Elemental Balances Material Balance Westinghouse (Wt. % Distribution) Studies-Laboratory Scale ______________________________________ Carbon: Shale Oil 31.0 30.6 26.7 29.7 33.6 Spent Shale NA 60.9 58.8 55.4 40.2 Product Gas** NA 1.1 2.7 3.3 NA Unaccounted 69.0 7.4 11.8 11.6 26.2 Hydrogen: Shale Oil 28.6 28.0 23.8 26.8 31.9 Spent Shale NA 32.3 40.2 23.3 20.5 Product Gas** NA 4.5 4.4 8.4 NA Unaccounted 61.4 35.2 31.6 41.5 47.6 Nitrogen: Shale Oil 18.4 19.7 17.3 20.1 25.4 Spent Shale NA 70.1 69.7 64.6 47.2 Product Gas** NA NA NA NA NA Unaccounted 81.6 10.1 13.0 15.3 27.4 Sulfur: Shale Oil 4.8 5.7 4.6 5.6 5.2 Spent Shale NA 75.4 55.7 62.3 55.2 Product Gas** NA NA NA NA NA Unaccounted 95.2 18.9 39.7 32.1 39.6 Ash: Spent Shale NA 99.2 100.7 100.3 99.0 Unaccounted -- 0.8 -0.7 -0.3 1.0 ______________________________________ *Unaccounted Depends on Products Collection and Analytical Precisions **In Westinghouse Studies the Gas Released is not Analyzed for C.sub.2 + Compounds, H.sub. 2 O, H.sub.2 S and NH.sub.3 Which can be Present in the Gas
The thrust of Burton's teaching is that sufficient oxygen is supplied to burn completely the residual carbon in the spent shale and/or a portion of the fuel products. Burton implies that the heat derived in this way may not be sufficient, as it suggests adding external heat. Attempts to recover liquid and gaseous fuel from Eastern shale by the practice taught by Burton and other like prior art has proven uneconomical. From a social standpoint, it is highly inadvisable to abandon the Eastern shale. It is estimated that Eastern shales primarily in Kentucky, Ohio, Tennessee, and Indiana hold some 3 trillion barrels including 400 billion barrels in rock which contains 20-25 gal/ton and which can be surface mined. The development of Eastern shales is facilitated by an available supply of water and the presence of workers and a social infrastructure.
It is an object of this invention to overcome the disadvantages and drawbacks of the prior art and to provide an economical process for recovering fuel from Eastern shale. It is also an object of this invention to provide apparatus for practicing this process.